1. Field of the Invention
The invention relates to a dendritic polymer, and more particularly to a magnetic resonance imaging contrast agent containing the dendritic polymer.
2. Description of the Related Art
Currently, medical imaging is capable of creating functional and anatomical images via physical signals of magnetic, photo (fluorescence, near-infrared, X-ray), and radioactive rays emitted by different imaging instruments. The imaging instruments include the Planar X-ray Imaging system, the X-ray Computerised Tomography (CT) system, and the Magnetic Resonance Imaging (MRI) system, which are utilized in the diagnosis of the central nervous system, skeletal nervous system, stomach, ribcage, and angiography, diagnosis of the biliary tractphotography, and the diagnosis of the mutation of tumor tissue. While the appearance of the anatomic tissue does not change, changes in blood circulation, cell activity, and metabolism of the diagnosed location do occur for many different clinical symptoms. Therefore, early detection of the location of illnesses can be accomplished by a highly sensitive Nuclear Imaging system.
Diethylenetriaminepentaacetic acid (DTPA) ligands are widely used in fundamental research as useful chelators in magnetic resonance imaging. The complexes reduce longitudinal and transverse relaxation times (T1 and T2 respectively) of water molecule protons, resulting in a pronounced contrast enhancement in a magnetic resonance image.
However, clinically used contrast agents such as Magnevist (gadolinium salt of DTPA) reveal a disadvantage. Immediately after intravenous application, Magnevist produced images clear quickly from the body through the glomerulus of the kidney and leakage from the vessels due to its low molecular weight compound. With the rapid clearance rate, physicians have limited time and ability to complete time-dependent imaging studies or obtain highly resolved images of patients. Meanwhile, low concentrations of small molecular contrast agents are unable to detect anomalies smaller than a few centimeters when using magnetic resonance imaging (MRI), thereby requiring high concentrations of the contrast agent.
Nevertheless, by using high concentrations, not only does the risk of toxicity caused by the highly concentrated heavy metal occur, but an abundance of molecular imaging agents will also abundantly accumulate. Thus, clinical applications are limited.
Accordingly, a significant topic of research in magnetic resonance imaging technology has been to develop a magnetic resonance imaging agent that efficiently targets the location of the illness by using lower magnetic resonance imaging agent dosages.
Thus, a high-molecular weight magnetic resonance imaging agent with multiple chelates has been developed to overcome the disadvantages such as the rapid clearance rate of the agent from the body and the need for high local small molecular contrast agent concentrations.